Systems and methods for assessing tissue contact

ABSTRACT

Systems and methods are disclosed for assessing tissue contact, e.g., for mapping, tissue ablation, or other procedures. An exemplary tissue contact sensing system comprises a flexible tip device. At least one piezoelectric sensor is housed within the flexible tip device. The at least one piezoelectric sensor is responsive to contact stress of the flexible tip device by generating electrical signals corresponding to the amount of contact stress. An output device is electrically connected to the at least one piezoelectric sensor. The output device receives the electrical signals for assessing tissue contact by the flexible tip device. Methods for assembling and using the flexible tip device are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/617,364, filed 28 Dec. 2006 (the '364 application), which is acontinuation-in-part of U.S. application Ser. No. 11/553,965, filed 27Oct. 2006, now U.S. Pat. No. 8,021,361 (the '965 application), whichclaims the benefit of U.S. provisional application No. 60/730,634, filed27 Oct. 2005 (the '634 application). This application is also acontinuation-in-part of U.S. application Ser. No. 11/549,100, filed 12Oct. 2006, now pending (the '100 application), which claims the benefitof U.S. provisional application No. 60/727,164, filed 13 Oct. 2005 (the'164 application), all of which are hereby incorporated by reference asthough fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention is directed toward assessing tissue contact forflexible tip devices which may be implemented for use with catheters,and methods of manufacturing and using the flexible tip devices forassessing tissue contact. In particular, the flexible tip devices of thepresent invention may comprise one or more piezoelectric sensors forassessing tissue contact for mapping, ablation or other procedures.

b. Background Art

Various devices (e.g., electrode sensors, thermal sensors, ablationelectrodes, etc.) may be implemented in catheters inserted into thepatient's body (e.g., the patient's heart) for use in a wide variety ofmedical procedures, such as “mapping” the interior of the heart, thermal“mapping,” and tissue ablation, to name only a few examples. It is oftendesirable to determine the level of tissue contact between the devicebeing used and the tissue the device is being used on.

By way of illustration, sensor output is only meaningful for mappingprocedures when the sensors are in sufficient contact with the tissuebeing mapped. “False” signals received when the sensor is not in good orsufficient contact with the tissue may result in inaccurate mapping ofthe tissue (e.g., the interior of a patient's heart).

By way of further illustration, it is desirable to control the level ofcontact to form ablative lesions. In particular, it is desirable tomaintain a constant level of contact between the ablation electrode andthe cardiac tissue in order to elevate tissue temperature to around 50°C. and form lesions in the cardiac tissue via coagulation necrosis. Suchlesions change the electrical properties of the cardiac tissue and maylessen or eliminate undesirable atrial fibrillations when formed atspecific locations in cardiac tissue. Insufficient contact during theablation procedure may result in poor lesion formation and/or damage tosurrounding tissue in the heart

Tissue contact is not always readily determined using conventionalfluoroscopy techniques. Instead, the physician determines tissue contactbased on his/her experience maneuvering the catheter. Such experienceonly comes with time, and may be quickly lost if the physician does notuse the catheter on a regular basis. When used inside the heart, thebeating heart further complicates matters by making it difficult toassess and maintain sufficient contact with the tissue for a sufficientlength of time. If contact with the tissue cannot be properlymaintained, advantages of using the device may not be fully realized.

BRIEF SUMMARY OF THE INVENTION

It is desirable to be able to assess tissue contact for variousprocedures, including but not limited to mapping and ablation procedureswithin the heart. Positioning a flexible tip device (e.g., a sensingelectrode, thermal sensor, ablation electrode, etc.) against a tissuecreates contact stresses, which may be measured by implementing one ormore piezoelectric sensors operatively associated with the flexible tipdevice. The piezoelectric sensor(s) generates a voltage signalcorresponding to the contact stresses.

In an exemplary embodiment, one or more piezoelectric sensor isoperatively associated with a flexible tip device. Output from thepiezoelectric sensor(s) enables a user (e.g., a physician or technician)to position the flexible tip device against a moving tissue with thedesired amount of pressure for the procedure.

An exemplary tissue contact sensing system comprises a flexible tipdevice. At least one piezoelectric sensor is housed within the flexibletip device. The at least one piezoelectric sensor is responsive tocontact stress of the flexible tip device by generating electricalsignals corresponding to the amount of contact stress. An output deviceis electrically connected to the at least one piezoelectric sensor. Theoutput device receives the electrical signals for assessing tissuecontact by the flexible tip device.

Another exemplary system comprises flexible tip means for practicing amedical procedure. The system also comprises means for generatingpiezoelectric signals corresponding to contact stress of the flexibletip means. The system also comprises means for assessing tissue contactof the flexible tip means based at least in part on the piezoelectricsignals.

An exemplary method of assessing tissue contact comprises: generatingpiezoelectric signals in response to stress caused by a flexible tipdevice contacting a tissue, and outputting piezoelectric signals forassessing tissue contact. Output may be conveyed to the user inreal-time (e.g., at a display device or other interface) so that theuser can properly position the flexible tip device on the tissue withthe desired level of contact for the procedure. For example, the usermay increase contact pressure if the output indicates insufficientcontact for the procedure. Or for example, the user may reduce contactpressure if the output indicates too much contact for the procedure.

An exemplary method for assembling a flexible tip device comprises:positioning a piezoelectric film into a lumen of the flexible tipdevice, applying a flexible polymer into the lumen of the flexible tipdevice to maintain a position of the piezoelectric film, and curing theflexible polymer. Optionally, the piezoelectric film may be formed intoa substantially J or U (or other desired shape) before applying theflexible polymer. More flexible polymer may be applied to thepiezoelectric film after curing to insulate the piezoelectric film.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a-c illustrate exemplary contact between a flexible tip deviceand a tissue.

FIG. 2 is a perspective view of an exemplary flexible tip deviceoperatively associated with a piezoelectric sensor for assessing tissuecontact.

FIG. 2 a is a side view of the flexible tip device shown in FIG. 2.

FIG. 2 b is a cross-sectional view of the flexible tip device takenalong lines 2 b-2 b in FIG. 2 a.

FIG. 3 a is a sectional view of an exemplary piezoelectric sensor whichmay be implemented in the flexible tip device. In FIG. 3 b-c, thepiezoelectric sensor is shown in exaggerated form as it may respond tovarious stresses.

FIG. 4 shows exemplary output of an oscilloscope showing a waveformcorresponding to electrical signals generated by a piezoelectric sensorfor assessing tissue contact.

FIGS. 5 and 5 a through FIGS. 10 and 10 a show alternative embodimentsfor implementing at least one piezoelectric sensor with a flexible tipdevice for assessing tissue contact.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of systems and methods to assess contact between aflexible tip device and a tissue are depicted in the figures. Exemplarysystems comprise a flexible tip device (e.g., sensing electrode, thermalsensor, or ablation electrode) which may be inserted into the patientusing a catheter. During an exemplary procedure, a user (e.g., thepatient's physician or a technician) may insert the catheter into one ofthe patient's blood vessels, e.g., through the leg or the patient'sneck. The user, guided by a real-time fluoroscopy imaging device, movesthe catheter to the desired position within the patient's body (e.g.,into the patient's heart).

When the catheter reaches the patient's heart, the flexible tip devicemay be used to perform various procedures, such as, electrically orthermally mapping the myocardium (i.e., muscular tissue in the heartwall), or tissue ablation procedures. Determining contact with thetissue is often critical. In ablation procedures, for example, theamount of contact is critical to form sufficiently deep ablative lesionson the tissue without damaging surrounding tissue in the heart.

As described further below, the system may include one or morepiezoelectric sensors which generate electric signals in response tostresses caused by contact with a surface (e.g., tissue within thebeating heart). Accordingly, embodiments of the present inventionprovide a number of advantages, including, for example, facilitatingenhanced tissue contact in difficult environments such as a movingsurface inside a beating heart.

FIG. 1 a-c illustrate exemplary contact between a flexible tip device 10(e.g., an electrode sensor, thermal sensor, or ablative electrode) and atissue 12 (e.g., myocardium). The flexible tip device 10 may be insertedthrough a shaft 14 of catheter 16. The catheter shaft 14 may be made ofa plastic or other suitable material which facilitates insertion intothe patient's body (e.g., the patient's heart) through the bloodvessels.

Optionally, the flexible tip device 10 may be electrically connected viasuitable wiring through the catheter shaft 14 to a generator (notshown), such as, e.g., a radio frequency (RF) generator. For example,where the flexible tip device 10 is an electrode, the RF generator isoperable to emit electrical energy (e.g., RF radiation) near the distalend of the electrode for mapping operations or forming ablation lesionson the tissue 12.

During use, a user may operate a handle portion (not shown) of thecatheter 16 to manually position the catheter 16 inside the patient'sbody, e.g., so that the flexible tip device 10 is in contact with thetissue 12. In FIGS. 1 a and 1 c, the flexible tip device 10 is shownhaving little, if any, contact with the tissue 12, e.g., the flexibletip device 10 may be “floating” adjacent the tissue 12. In FIG. 1 b, theflexible tip device 10 is shown in contact with the tissue 12.

When the flexible tip device 10 is in sufficient or “good” contact withthe tissue 12, the flexible tip device 10 may move or be deflected bymovement of the tissue 12 generally in the directions illustrated byarrows 18. Movement of the flexible tip device 10 may be measured inreal-time using at least one piezoelectric sensor 20 to assess contactwith the tissue 12, as described more fully below.

Before continuing, it is noted that the contact and motion illustratedin FIG. 1 b is shown for purposes of illustration and is not intended tobe limiting. Other contact and motion may also exist and/or be desiredby the user. The definition of sufficient or “good” contact may dependat least to some extent on the procedure being performed and/or variousoperating conditions, such as, e.g., the type of tissue, desired depthof the ablation lesion, and power and duration of the applied RF energy,to name only a few examples.

It is also noted that other components typical of systems which areconventionally implemented for various procedures, are not shown ordescribed herein for purposes of brevity. Such components maynevertheless also be provided as part of, or for use with, the flexibletip device 10. For example, these systems commonly include or are usedin conjunction with an ECG recording system, and/or various controls forperforming the procedure. Such components are well understood in themedical devices arts and therefore further explanation is not necessaryfor a complete understanding of the invention.

As previously mentioned, one or more piezoelectric sensors 20 may beoperatively associated with the flexible tip device 10 to measure stresswhen the flexible tip device 10 is in contact with the tissue 12. FIG. 2is a perspective view of a distal tip portion (e.g., the portion shownin contact with the tissue 12 in FIG. 1 b) of an exemplary flexible tipdevice 10 operatively associated with a piezoelectric sensor 20 forassessing tissue contact. FIG. 2 a is a side view of the flexible tipdevice 10 shown in FIG. 2. FIG. 2 b is a cross-sectional view of theflexible tip device 10 taken along lines 2 b-2 b in FIG. 2 a. In thisembodiment, the piezoelectric sensor 20 is substantially U-shaped,although other shapes are also contemplated as being within the scope ofthe invention.

In an exemplary embodiment, the piezoelectric sensor 20 may include apiezoelectric film 21 laminated on a support structure 22 anchoredwithin the flexible tip device 10. Optionally, piezoelectric film may belaminated to opposite sides of the support structure 22. Signals fromthe piezoelectric films on opposite sides of the support structure 22may be combined to improve the sensitivity of the contact sensing.Additionally, because the stress response of piezoelectric materials isanisotropic, the two sides may be oriented differently with respect toeach other to either attenuate directional differences in sensitivity orprovide directional information of the tissue contact.

Other means for supporting the piezoelectric sensor 20 within theflexible tip device 10 are also contemplated. For example, thepiezoelectric sensor 20 may be provided without the support structure 22and integrally molded within the flexible tip device 10. These and othermethods for providing the piezoelectric sensor 20 in the flexible tipdevice 10 will be readily apparent to those having ordinary skill in theart after becoming familiar with the teachings herein.

The piezoelectric sensor 20 may be provided within a flexible polymer orcompliant section 26 of the flexible tip device 10. In addition tohousing the piezoelectric sensor 20 in the flexible tip device 10, andprotecting the piezoelectric sensor 20 from external damage orcorrosion, the compliant section 26 may serve as a low pass mechanicalfilter. That is, the compliant section 26 attenuates high frequency“noise” signals caused, e.g., by minor vibrations from intermittentcontact during positioning of the flexible tip device 10 adjacent thetissue 12. Accordingly, high frequency noise signals are damped, or evennon-existent, as output for the user. However, the piezoelectric sensor20 does not need to be provided in a compliant section. For example, thepiezoelectric sensor 20 may instead be provided within an airspaceformed in the flexible tip device 10.

Electrical wiring (not shown) may be connected to the piezoelectricsensor 20 and a ground. The electrical wiring may extend through thelumen of the flexible tip device 10 to deliver electrical signals fromthe piezoelectric sensor 20 to a data acquisition/processing/outputdevice (also not shown), such as, e.g., an echocardiogram (ECG) device.Alternatively, a wireless connection may be implemented, e.g., byproviding a transmitter in the catheter and a receiver in associationwith the data acquisition/processing/output device.

In an exemplary embodiment, the flexible tip device 10 may be assembledas follows. A strip of piezoelectric film 21 is laminated to the supportstructure 22 and then formed (e.g., bent) into the desired shape (e.g.,the substantially U-shape shown in FIG. 2). The formed piezoelectricsensor 20 may then be positioned in the lumen of the flexible tip device10. While the laminated piezoelectric film is in the desired positionwithin the lumen of the flexible tip device 10, a flexible polymer(e.g., flexible ultraviolet (UV) adhesive) may be applied into the lumenof the flexible tip device 10 to hold the ends of the piezoelectricsensor 20 in place so that it does not move and maintains the desiredshape (e.g., the substantially U-shape). The adhesive may then be cured(e.g., using UV light). More adhesive may then be applied around theremainder of the piezoelectric sensor 20 so that it covers or insulatesthe piezoelectric sensor 20. The additional adhesive may then be curedto form compliant section 26.

It is noted that the configuration with the piezoelectric sensor 20housed within the flexible tip device 10 enable manufacturing ofrelatively small sizes and therefore are particularly suitable for use,e.g., in so-called brush electrodes. However, these embodiments are notlimited to any particular size or use. It is also noted that othershapes and arrangements of the piezoelectric sensor(s) 20 are alsocontemplated, as will be readily apparent to those having ordinary skillin the art after becoming familiar with the teachings herein.

In use, the piezoelectric sensor 20 responds to electrode-tissue contactstresses by generating electrical energy (e.g., a voltage). Accordingly,when the flexible tip device 10 is positioned in contact with the tissue12, piezoelectric sensor 20 generates an electrical signal correspondingto stress caused by this contact. The resulting electrical signal may beprocessed and/or otherwise output for the user so that the user is ableto determine when the flexible tip device 10 contacts the tissue 12.

Piezoelectric sensors which generate electrical energy in response toapplied mechanical stress are well-understood in the electro-mechanicalarts. In general, piezoelectric sensors comprise a piezoelectricmaterial which contains positive and negative electrical charges. In aneutral or “non-stressed” state, these electrical charges aresymmetrically distributed in the piezoelectric material such that thematerial exhibits an overall neutral electrical charge. However,subjecting the piezoelectric material to a mechanical stress (e.g.,flexure, pressure, and/or tension) disturbs the symmetrical distributionof electrical charges, thereby generating electrical energy across thematerial. Even minor deformation of some piezoelectric materials (e.g.,on the order of nanometers) may generate a measurable voltage signal.Operation of piezoelectric material may be better understood with briefreference to FIG. 3 a-c

FIG. 3 a is a cross-sectional perspective view of a portion of anexemplary piezoelectric sensor 20 which may be implemented in theflexible tip device. In FIG. 3 b-c, the piezoelectric sensor 20 is shownin exaggerated form as it may respond to various stresses, wherein FIG.3 b is a side-view of the piezoelectric sensor 20 shown in FIG. 3 a, andFIG. 3 c is a top-view of the piezoelectric sensor 20 shown in FIG. 3 a.

In an exemplary embodiment, the piezoelectric sensor 20 may be alaminated sensor or film having a plurality of laminated layers.Although not required, laminating the sensor increases its sensitivity.Piezoelectric films are flexible, lightweight, and tough engineeredplastic that is available in a wide variety of thicknesses and largeareas. Among other advantages, piezoelectric film has a low acousticimpedance which is close to that of water, human tissue, and otherorganic materials. For example, the acoustic impedance of piezoelectricfilm is only about 2.6 times the acoustic impedance of water.Piezoelectric film also has a low density and excellent sensitivity, andis mechanically tough. When extruded into a thin film, piezoelectricpolymers can be directly attached to a support structure withoutdistributing its mechanical range of motion. Piezoelectric film istherefore well suited to strain-sensing applications requiring very widebandwidth and high sensitivity.

In FIG. 3 a, the laminated layers of piezoelectric sensor 20 maycomprise a piezoelectric material 30 “sandwiched” between metal layers32 a and 32 b and protective coating 34 a and 34 b. Metal layers 32 aand 32 b may be any suitable metal, e.g., a thin layer of silver ink.The metal layers 32 a and 32 b serve to collect electrical chargegenerated by the piezoelectric material 30, e.g., for delivery aselectrical signals via electrical wiring to a dataacquisition/processing/output device. Metal layers 32 a and 32 b serveto collect electrical energy in response to stress of the piezoelectricmaterial 30. Piezoelectric material, such as PVDF (Kynar), iscommercially available as a highly-sensitive, thin, flexible polymerfilm, which makes it particularly desirable for use with deflectablecatheters. Protective coating 34 a and 34 b may be any suitablematerial, e.g., Mylar®.

It is noted that the laminated layers of piezoelectric sensor 20 are notlimited to any particular material and/or configuration. For example,the piezoelectric sensor 20 is not limited to use with separate metallayers 32 a and 32 b. Nor is the piezoelectric sensor 20 limited to thegenerally rectangular configuration shown in FIG. 3 a.

In an exemplary embodiment, the piezoelectric material 30 may comprise athin, flexible, polymer-based material. One such piezoelectric film is apolyvinylidene fluoride (PVDF) film commercially available from theSensor Products Division of Measurement Specialties, Inc. (Norristown,Pa.). This PVDF film is approximately 28 μm thick, enabling the PVDFfilm to be readily housed within the catheter shaft 14.

In addition, this PVDF film has a wide frequency range of about 0.001 Hzto 10⁹ Hz and a high dynamic stress constant (g₃₁=216×10⁻³ Vm/N). Forpurposes of illustration, other common piezoelectric materials, such aslead zirconate titanate (PZT) has a dynamic stress constant(g₃₁) of10×10⁻³ Vm/N, and barium titanium oxide (BaTiO₃) has a dynamic stressconstant(g₃₁) of 5×10⁻³ Vm/N. Accordingly, the PVDF film is verysensitive, exhibiting a relatively high voltage response to relativelysmall mechanical stresses, and is therefore well-suited for measuringdynamic stresses and strains.

Of course the piezoelectric sensor 20 described above with reference toFIG. 3 a is for purposes of illustration and not intended to belimiting. Other piezoelectric sensors may also be implemented, and arenot limited to laminated piezoelectric film. Nor are piezoelectricsensors limited to use with any particular type or size of piezoelectricmaterial. Selection of piezoelectric sensor 20 for use with the flexibletip device 10 may be application-specific and depend at least in part onone or more design considerations, such as, but not limited to, thedesired sensitivity and/or spatial constraints for housing thepiezoelectric sensor.

Piezoelectric sensor 20 is shown in FIG. 3 a in a neutral state. In theneutral state, the piezoelectric material 30 is not subject to anystresses or strains. Accordingly, the electrical charges aresymmetrically distributed on either side of the neutral plane N in thepiezoelectric material 30 such that the material exhibits an overallneutral electrical charge.

The most widely used coefficients, d3n (for charge) and g3n (forvoltage), possess two subscripts. The first refers to the electricalaxis, while the second subscript refers to the mechanical axis. Becausepiezoelectric film is thin, the electrodes are only applied to the topand bottom film surfaces. Accordingly, the electrical axis is alwaysreferred to as “3”, as the charge or voltage is always transferredthrough the thickness (n=3) of the film. The mechanical axis can beeither 1, 2, or 3, because the stress can be applied to any of theseaxes. Typically, piezoelectric film is used in the mechanical 1direction for low frequency sensing and actuation (<100 KHz) and in themechanical 3 direction for high ultrasound sensing and actuation (>100KHz). These stresses can be better understood with reference to FIGS. 3b and 3 c.

FIG. 3 b is a side-view of the piezoelectric sensor 20 shown in FIG. 3a. In FIG. 3 b, the piezoelectric sensor 20 is shown in exaggerated formas it may respond to transverse stresses applied generally in thedirection of arrow 36. In this stressed state, the piezoelectricmaterial 30 undergoes transverse strain relative to its neutral state,as illustrated by arrows A1 and A2. The piezoelectric sensor 20 may alsorespond to bending stresses. In this stressed state, the piezoelectricmaterial 30 undergoes flexural strain relative to its neutral state, asillustrated by arrows B1 and B2.

FIG. 3 c is a top-view of the piezoelectric sensor 20 shown in FIG. 3 a.In FIG. 3 c, the piezoelectric sensor 20 is shown in exaggerated form asit may respond to longitudinal stresses applied generally in thedirection of arrows 37 a and 37 b. In this stressed state, thepiezoelectric material 30 is longitudinally strained relative to itsneutral state, as illustrated by arrows C1 and C2.

In each case, these stresses disturb the symmetrical distribution ofelectrical charges, and electrical energy is generated across thepiezoelectric material 30. In operation, this electrical energy may becollected by metal layers 32 a, 32 b, e.g., for delivery as anelectrical signal via electrical wiring through the catheter shaft 14 toa data acquisition/processing/output device (not shown).

Returning to the piezoelectric sensor 20 shown mounted to the flexibletip device 10 in FIG. 2, it can be readily seen that piezoelectricsensor 20 is stressed or strained due to stress in the directionsillustrated by arrows 18. The piezoelectric sensor 20 responds bygenerating electrical (voltage) signals. These electrical signals may beviewed by the user, e.g., as output on an electrical monitoring device.

FIG. 4 is exemplary output of an oscilloscope showing waveform 42corresponding to electrical signals generated by a piezoelectric sensor20 when the flexible tip device 10 is in contact with a moving tissue12, such as the myocardium (e.g., as shown in FIG. 1 b). Duringoperation, output such as waveform 42 may be displayed for a user, e.g.,as a waveform on an ECG device.

In an exemplary embodiment, the signal strength (e.g., amplitude) fromthe piezoelectric sensor 20 is proportional to the amount of stress dueto the contact of the flexible tip device 10 with tissue 12 (e.g., themyocardium), and therefore can be used to determine if the flexible tipdevice 10 is in good contact with the tissue 12. If the contact isinsufficient for the procedure, then there are no peaks in the resultingwaveform 42 (or the peaks are intermittent). On the other hand, a strongcorrelation between the heartbeat and output by the piezoelectric sensorindicates sufficient or good contact with the moving tissue.

Signal periodicity is also a strong indicator of dynamic contactassessment. For example, if the period between heartbeats correspondswell with the period output by the piezoelectric sensor 20, stresses onthe piezoelectric sensor 20 are being caused by the heartbeat (and notsome other reason). Accordingly, the user may use this feedback to movethe flexible tip device 10 to achieve the desired tissue contact.

Before continuing, it is noted that any suitable analog and/or digitaldevice may be implemented for indicating tissue contact to a user. Inanother exemplary embodiment, the electrical signals generated bypiezoelectric sensor 20 may be further characterized using a suitableprocessing device such as, but not limited to, a desktop or laptopcomputer. Such processing device may be implemented to receive thevoltage signal generated by the piezoelectric sensor 20 and convert itto a corresponding contact condition and output for the user, e.g., at adisplay device.

It is also noted that the output device is not limited to a displaydevice. For example, the tissue contact may be output to the user as anaudio signal or tactile feedback (e.g., vibrations) on the handle of thecatheter 16. In any event, circuitry for conveying output of thepiezoelectric sensor to a user in one form or another may be readilyprovided by those having ordinary skill in the electronics arts afterbecoming familiar with the teachings herein.

Although the flexible tip device 10 shown in FIG. 2 can bend in anyangle and the piezoelectric sensor 20 still generates a signal, thepiezoelectric sensor 20 is not as sensitive in directions other thanthose illustrated by arrows 18. That is, the piezoelectric sensor 20 ismost sensitive if it is positioned or moved in a uni-planar directionfrom the position where the flat surface of the piezoelectric sensor 20is facing.

To receive a signal from other directions of movement, a twisted (e.g.,quarter-twisted) piezoelectric sensor may be implemented within theflexible tip device. Alternatively, multiple piezoelectric sensors 20(or strips of piezoelectric film) may be provided within the flexibletip device 10 to receive signals in bi-planar and full-arc multi-planarorientations, as discussed in the following embodiments.

FIGS. 5 and 5 a through FIGS. 10 and 10 a show alternative embodimentsfor implementing at least one piezoelectric sensor with a flexible tipdevice for assessing tissue-contact. It is noted that 100-series through600-series reference numbers are used in the embodiments shown in FIGS.5 and 5 a through FIGS. 10 and 10 a, respectively, to refer to likeelements described above with reference to FIGS. 2 and 2 a-b. Thereforethe description of some elements may not be repeated in the followingdiscussion.

FIG. 5 is a side view of a flexible tip device 110 showing twopiezoelectric sensors 120 a-b. FIG. 5 a is a cross-sectional view of theflexible tip device 110 taken along lines 5 a-5 a in FIG. 5. In thisembodiment, the piezoelectric sensors 120 a-b are mounted substantiallyperpendicular to one another.

In use, the piezoelectric sensors 120 a-b respond to mechanical stressesby generating electrical energy (e.g., a voltage) which may be output toa user (e.g., as illustrated in FIG. 4). In addition to detecting tissuecontact, the relative magnitude and direction of the signal obtainedfrom each of the separate piezoelectric sensors 120 a-b may be used todetermine the direction and plane of contact of the flexible tip device110. The resulting electrical signal may be processed and/or otherwiseoutput for the user so that the user is able to determine the desiredlevel of contact with the tissue 12.

FIG. 6 is a side view of a flexible tip device 210 showing threepiezoelectric sensors 220 a-c. FIG. 6 a is a cross-sectional view of theflexible tip device 210 taken along lines 6 a-6 a in FIG. 6. In thisembodiment, the piezoelectric sensors 220 a-c are mounted at about 30°relative to one another.

In use, the piezoelectric sensors 220 a-c respond to mechanical stressesby generating electrical energy (e.g., a voltage) which may be output toa user (e.g., as illustrated in FIG. 4). In addition to detecting tissuecontact, the relative magnitude and direction of the signal obtainedfrom each of the separate piezoelectric sensors 220 a-c may be used todetermine the direction and plane of contact of the flexible tip device210. The resulting electrical signal may be processed and/or otherwiseoutput for the user so that the user is able to determine the desiredlevel of contact with the tissue 12.

FIG. 7 is a side view of a flexible tip device 310 showing threeseparate piezoelectric sensors 320 a-c. FIG. 7 a is a cross-sectionalview of the flexible tip device 310 taken along lines 7 a-7 a in FIG. 7.In this embodiment, the separate piezoelectric sensors 320 a-c aresubstantially hook or J-shaped and mounted at about 120° relative to oneanother. This embodiment enables both axial and angular (or radial)stresses to be detected during operation. In addition, the openingformed through the center of the piezoelectric sensors 320 a-c may beused with irrigated electrodes.

In use, the piezoelectric sensors 320 a-c respond to mechanical stressesby generating electrical energy (e.g., a voltage) which may be output toa user (e.g., as illustrated in FIG. 4). In addition to detecting tissuecontact, the relative magnitude and direction of the signal obtainedfrom each of the separate piezoelectric sensors 320 a-c may be used todetermine the direction and plane of contact of the flexible tip device310. The resulting electrical signal may be processed and/or otherwiseoutput for the user so that the user is able to determine the desiredlevel of contact with the tissue 12.

FIG. 8 is a side view of a flexible tip device 410 showing six separatepiezoelectric sensors 420 a-f. FIG. 8 a is a cross-sectional view of theflexible tip device 410 taken along lines 8 a-8 a in FIG. 8. In thisembodiment, the separate piezoelectric sensors 420 a-f are substantiallyhook or J-shaped and mounted at about 30° relative to one another.

In use, the piezoelectric sensors 420 a-f respond to mechanical stressesby generating electrical energy (e.g., a voltage) which may be output toa user (e.g., as illustrated in FIG. 4). In addition to detecting tissuecontact, the relative magnitude and direction of the signal obtainedfrom each of the separate piezoelectric sensors 420 a-f may be used todetermine the direction and plane of contact of the flexible tip device410. The resulting electrical signal may be processed and/or otherwiseoutput for the user so that the user is able to determine the desiredlevel of contact with the tissue 12.

In each of the embodiments shown in FIGS. 5 and 5 a through FIGS. 8 and8 a, the compliant section is non-conductive. Accordingly, if theflexible tip device is implemented as an electrode, a separate electrodematerial may be provided through the shaft and into the distal portionof the flexible tip device. Alternatively, the distal portion of theflexible tip device may include a conductive material integrally formedas part of the flexible tip device to deliver RF energy during theprocedure (e.g., for mapping or ablation), as explained in more detailbelow with reference to the embodiments shown in FIGS. 9 and 9 a throughFIGS. 10 and 10 a.

FIG. 9 is a side view of a flexible tip device 510 showing six separatepiezoelectric sensors 520 a-f. FIG. 9 a is a cross-sectional view of theflexible tip device 510 taken along lines 9 a-9 a in FIG. 9. In thisembodiment, the separate piezoelectric sensors 520 a-f are substantiallyhook or J-shaped and mounted at about 30° relative to one another. Inaddition, each of the piezoelectric sensors 520 a-f are individuallyinsulated (insulation 523 a-f) and provided in a conductive compliantsection 526. In use, the conductive compliant section 526 may be use todeliver RF energy during the procedure (e.g., for mapping or ablation).

FIG. 10 is a side view of a flexible tip device 610 showing six separatepiezoelectric sensors 620 a-f. FIG. 10 a is a cross-sectional view ofthe flexible tip device 610 taken along lines 10 a-10 a in FIG. 10. Inthis embodiment, the separate piezoelectric sensors 620 a-f aresubstantially hook or J-shaped and mounted at about 30° relative to oneanother and provided in a non-conductive compliant section 626. Inaddition, a conductive layer 624 may be provided surrounding thenon-conductive compliant section 626. A non-conductive shield 625 isprovided between the shaft 627 of the flexible tip device 610 and theconductive layer 624 to insulate the conductive layer 624 along thelength of the shaft 627 except at the distal or tip portion of theflexible tip device 610 for delivering RF energy. In use, the conductivelayer may be use to deliver RF energy during the procedure (e.g., formapping or ablation) and the non-conductive compliant section 626 servesto insulate the piezoelectric sensors 620 a-f.

It is noted that still more piezoelectric sensors in addition to thoseshown in FIGS. 5 and 5 a through FIGS. 10 and 10 a may be implemented inother embodiments. Additional piezoelectric sensors may serve toincrease the sensitivity of the output. Likewise, the piezoelectricsensors may be positioned relative to one another in any suitable mannerand the positioning is not limited to the orientations shown in thefigures. The number and positioning of piezoelectric sensors may dependat least to some extent on various design considerations, such as thedesired sensitivity, size, and cost of the flexible tip device, as willbe readily understood by those having ordinary skill in the art afterbecoming familiar with the teachings herein.

Although several embodiments of this invention have been described abovewith a certain degree of particularity, those skilled in the art couldmake numerous alterations to the disclosed embodiments without departingfrom the spirit or scope of this invention. References are only used foridentification purposes to aid the reader's understanding of the presentinvention, and do not create limitations as to the position,orientation, or use of the invention. In addition, various combinationsof the embodiments shown are also contemplated even if not particularlydescribed. Changes in detail or structure, such as but not limited tocombinations of various aspects of the disclosed embodiments, may bemade without departing from the spirit of the invention as defined inthe appended claims.

1-26. (canceled)
 27. A tissue contact sensing system comprising: aplurality of piezoelectric sensors extending in a direction coaxial to acentral longitudinal axis of a shaft and offset by about 120 degreeswithin a flexible tip of the shaft; and an output device electricallyconnected to the piezoelectric sensors, the output device receivingelectrical signals generated in response to contact stress of theflexible tip for assessing tissue contact.
 28. The tissue contactsensing system of claim 27, wherein the piezoelectric sensors arearranged within the flexible tip to detect axial stress.
 29. The tissuecontact sensing system of claim 27, wherein the piezoelectric sensorsare arranged within the flexible tip to detect angular stress.
 30. Thetissue contact sensing system of claim 27, wherein the piezoelectricsensors are arranged within the flexible tip to detect radial stress.31. The tissue contact sensing system of claim 27, wherein thepiezoelectric sensors are arranged within the flexible tip to detectboth axial stress and angular stress.
 32. The tissue contact sensingsystem of claim 27, further comprising an opening formed through acenter of the piezoelectric sensors.
 33. The tissue contact sensingsystem of claim 27, wherein the piezoelectric sensors are arranged toprovide an irrigation path to irrigated electrodes in the flexible tip.34. The tissue contact sen g system of claim 27, wherein thepiezoelectric sensors are individually insulated.
 35. The tissue contactsensing system of claim 27, wherein the piezoelectric sensors areprovided in a conductive compliant section.
 36. The tissue contactsensing system of claim 27, further comprising a conductive layersurrounding a non-conductive compliant section of the flexible tip. 37.The tissue contact sensing system of claim 27, further comprising anon-conductive shield between the shaft and the flexible tip and aconductive layer.
 38. The tissue contact sensing system of claim 37,wherein the non-conductive shield insulates the conductive layer along alength of the shaft except at a distal portion of the flexible tip fordelivering radio frequency (RF) energy.
 39. The tissue contact sensingsystem of claim 3, wherein the conductive layer is configured todelivery RF energy.
 40. The tissue contact sensing system of claim 39,wherein the non-conductive compliant section is configured to insulatethe piezoelectric sensors.
 41. A catheter comprising: a plurality ofpiezoelectric sensors extending in a direction coaxial to a centrallongitudinal axis of a shaft and offset by about 120 degrees within aflexible tip of the shaft, the plurality of piezoelectric sensorsgenerating electrical signals generated in response to contact stress ofthe flexible tip for assessing tissue contact.
 42. The catheter of claim41, wherein the piezoelectric sensors are arranged within the flexibletip to detect at least one of axial stress, angular stress, and radialstress.
 43. The catheter of claim 41, wherein the piezoelectric sensorsare individually insulated.
 44. The catheter of claim 41, wherein thepiezoelectric sensors are provided in a conductive compliant section.45. The catheter of claim 41, further comprising a conductive layersurrounding a non-conductive compliant section of the flexible tip, anda non-conductive shield between the shaft and the flexible tip and aconductive layer, wherein the non-conductive shield insulates theconductive layer along a length of the shaft except at a distal portionof the flexible tip for delivering radio frequency (RF) energy.
 46. Acatheter with tissue contact assessment, comprising: a conductive layersurrounding a non-conductive compliant section of a flexible tip; and aplurality of piezoelectric sensors offset by about 120 degrees withinthe non-conductive compliant section of the flexible tip, the pluralityof piezoelectric sensors generating electrical signals generated inresponse to contact stress of the flexible tip to detect at least one ofaxial stress, angular stress, and radial stress.